The LandScan 2009 global population data set is a worldwide population database compiled on a 30" X 30" latitude/longitude grid. Census counts (at sub-national level) were apportioned to each grid cell based on likelihood coefficients, which are based on proximity to roads, slope, land cover, nighttime lights, and other data sets. LandScan has been developed as part of the Oak Ridge National Laboratory (ORNL) Global Population Project for estimating ambient populations at risk. The LandScan files are available via the internet in ESRI grid format by continent and for the world. At approximately 1 km resolution (30" X 30"), There is also a "Layer" file (lspop2000.lyr) for ArcGIS. LandScan is the finest resolution global population distribution data available and represents an ambient population (average over 24 hours). This dataset is part of the LandScan 2000 Global Population Database (2000-2010).Developed for the U. S. Department of Defense. "The values of the cells are integer population counts representing an average, or ambient, population distribution. An ambient population integrates diurnal movements and collective travel habits into a single measure (Dobson et al. 2000). Since natural or man made emergencies may occur at any time of the day, the goal of the LandScan model is to develop a population distribution surface in totality, not just the locations of where people sleep. Because of this ambient nature, care should be taken with direct comparisons of LandScan data with other population distribution surfaces." --from the Oak Ridge National Laboratory LandScan Web site, Sept. 12, 2013.